Thermodynamic study of retention in liquid exclusion–adsorption chromatography

The retention behaviour of fatty alcohol ethoxylates and fatty acid methyl ester ethoxylates on various reversed-phase columns in acetone–water has been studied in the regime of liquid exclusion–adsorption chromatography at different temperatures. Straight lines were obtained in the van’t Hoff plots. The entropy and enthalpy changes were found to be negative (at least in the range of lower oligomers) and showed a dependence of the number of oxyethylene units. For higher oligomers, both entropy and enthalpy changes approach a constant value. This can be explained by the existence of a rather thick layer of organic solvent close to the surface of the stationary phase.